"Although I don't believe this is widespread, it is cause for concern and I sincerely hope by highlighting this issue we can ensure such unscrupulous behaviour does not take root. The giving of alms is an important part of our faith, for people to try and abuse that is disappointing. If anybody witnesses this, they should report it to the authorities straight away," he added.

The council has warned its City Guardians and City Inspectors to keep an eye out for bogus beggars.

Cllr Daniel Astaire, cabinet member for community protection, said: "We're extremely concerned that Muslims may be exploited during the holy month of Ramadan. It is both immoral and unacceptable for people to prey on the generosity and benevolence of the Muslim community at this or any time."

Last year Westminster's Muslim community was targeted by dodgy traders trying to sell fake holy water claimed to be from a sacred well in Mecca. Environmental health officers seized a consignment from a shop in the Notting Hill area at the start of the holy month of Ramadan. Saudi authorities expressly forbid the commercial export of genuine holy Zam Zam water, so any being offered for sale in the UK will be from unauthorised sources and potentially harmful.

Ramadan began on September 1 and will continue for 29 or 30 days until September 29 or 30.